It is old, as shown in U.S. Pat. Nos. 3,460,614 and 3,701,549, to provide a valve assembly for use in a subsea well control system. However, in prior art devices valve pockets were drilled into a solid circular valve block, which was difficult to machine, extremely bulky, and required replacement of the entire unit if one of the pockets became damaged. Additionally, while the valve assemblies of the prior art were generally satisfactory for controlling a minimum number of underwater functions, subsea well control systems now control up to sixty four functions and require larger fluid passageways and valves for satisfactorily operating the underwater equipment, which cannot be accomplished in the prior art devices.
The present invention is directed to various improvements in a valve assembly for controlling flow of hydraulic fluid through the control passageways of a subsea control system.